Scalable optical switches and switching modules

ABSTRACT

Telecommunications switches are presented, including expandable optical switches that allow for a switch of N inputs×M outputs to be expanded arbitrarily to a new number of N inputs and/or a new number of M outputs. Switches having internal switch blocks controlling signal bypass lines are also provided, with these switches being useful for the expandable switches.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional applications61/552,616 filed on Oct. 28, 2011 to Vorobeichik et al., enabled“Scalable Optical Switches and Switching Modules,” 61/594,539 filed onFeb. 3, 2012 to Way et al., entitled “Scalable Optical Switches andSwitching Modules,” and 61/642,280 filed on May 3, 2012 to Way et al.,emitted “Scalable Optical Switches and Switching Modules,” all three ofwhich are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The technical field of the invention relates to a scalable system ofoptical switches based on optical switch devices that are constructed inmodular form for expansion of the switch system to achieve desiredswitching capability for an optical communication system. The inventionfurther relates to optical networks incorporating expandable modularoptical switching capability.

BACKGROUND OF THE INVENTION

Modern optical communications networks are universally used tointerconnect distant, regional, and metropolitan communications hubs fordirecting numerous diverse streams of telephony, digital video,internet, and other types of digital data. The means for mostefficiently and economically managing the ever-increasing capacity andspeed, demands on these networks, many communications channels areaggregated into streams each carrying up to 10 gigabits per second,presently emerging 40 and 100 gigabits per second, and future prospectsfor multiple hundreds of gigabits per second per aggregated data stream.Dozens of these data streams are transmitted simultaneously through eachfiber in the network utilizing wavelength-division multiplexing (WDM)where each stream is carried by an optical signal having an opticalwavelength slightly different but fully distinguishable from all theother wavelengths for the other streams in the fiber. These opticalstreams are routinely combined and separated as appropriate by variouswell-known optical fiber components at each end of the optical fiberlink.

These optical networks include many locations where optical fibersintersect at ‘nodes’. These nodes are in many ways analogous to theintersections of a complex highway system. Much traffic comes to thenode along each of the fibers, but not all the traffic on any fiber isnecessarily bound for the same destination. Some of the traffic may bebound for destinations local to the node, there may be new trafficoriginating local to the node, and other traffic may need to beindependently rerouted among the various outbound fibers from the node.Effecting the necessary reconfiguration of traffic at these nodes isprovided by switches.

Until recently, the primary means to provide such switching would beelectronic. To accomplish this, every wavelength in each fiber would beseparated to individual physical channels, and then the data in each ofthose wavelengths would be converted by an optical receiver into binaryelectrical data. Once all the data is in electrical form it can be pipedinto an electronic switching matrix in any of numerous possibleconfigurations, and reorganized into appropriate groupings on multipleoutput channels. Then the data in each output channel is converted backto optical by an optical transmitter at each output having a specificpredetermined wavelength and the data streams on distinct wavelengthsbound for each output fiber are remultiplexed and inserted into thatfiber. There may also be input and output data streams associated withlocal traffic that can be integrated with the data passing through thenode using additional ports on the switching matrix. At the data ratesused in each wavelength, electro-optic receivers and transmitters arerelatively expensive, bulky, and power hungry as compared to purelyoptical dispatch. Also, within an electrical switch matrix, electricalpower is required to push each and every bit of data through the matrix,and there may be hundreds of billions or trillions of bits movingthrough the matrix every second. In principle, electronic switching canprovide the ultimate flexibility in reconfiguring, formatting,synchronizing, and otherwise optimizing the presentation of the databefore sending it on its way. However, for the amount of data passingthrough a modern node, it is far and away simply impractical to switcheverything electronically, and the economics of providing thefundamental hardware is also unsupportable. Furthermore, the bandwidthpassing through the nodes is only expected to increase with time.

In the decade or so preceding this application, optical switchingtechnology has been emerging to complement the electronic switching inconcurrence with, and in fact enabling the increase in bandwidth of thedata passing through the nodes. Optical switching generally treats eachwavelength as a cohesive unit and passes each wavelength transparentlyto its destination within the node, either an output fiber or awavelength channel associated with local traffic. The transparentoptical switch effectively establishes a physical path for the light atthe specified wavelength on the specified input fiber to be passedlinearly and directly to the desired output fiber or local port. Such aswitch essentially passes any optical data regardless or format orcontent as long as it is within the optical wavelength range specifiedfor that optical channel. Since the optical switch cannot modify thedetailed data within the optical wavelength, it is not as flexible asart electronic switch. But more significantly, the power repaired toswitch the data for that wavelength is merely the amount of power neededto establish and maintain the optical path through the switch, which isgenerally orders of magnitude less than required for electronicallyswitching the same data. As power consumption is often the limitingfactor for the bandwidth that can be managed by a node, opticalswitching is not merely a convenience of remote configuration, butclearly enables the current and future performance levels of opticalnetworks.

SUMMARY OF THE INVENTION

One well-accepted approach whereby electronic switching providespractical scalability is through modular expansion. A basin switchingmodule is provided that supports the needs of a modest-sized switch.When a larger size switch is desired, instead of creating an additionalcomponent providing the new desired switch size, it is possible tointerconnect multiple modules of the expandable switch and communicationbetween the modules enables the set of modules to function as a largerswitch. Prior to this invention, optical switching components wereunable to provide a useful analogous capability. Optical switchingcomponents are generally cascadable by connecting the standard outputsof one component to the standard inputs of additional components.However this only provides for geometric expansion, i.e. 8 1×8 switchescan be cascaded off of a single 1×8 switch to create a 1×64 switch. Thisgeometric progression becomes too large too quickly to be of much use,and does not really provide what is needed for a modular, expandableswitch. The object of the present invention is to provide a means tosupport linear expansion of integrated optical switching arrays andmodules. The technical findings of these innovations reveal that a smallfraction of additional optical circuit elements on the schematicperiphery of the main optical circuitry for an optical switchingcomponent can provide expansion ports that allow multiple modules to beinterconnected in linear configurations, and these expansion portsenable the needed communications between the optical switchingcomponents to make linear expansion practical. The principles of theinnovations described herein can be applied to provide expansioncapability to a variety of common optical switching architectures. Thusthe innovations of the present invention enable scalable opticalswitching systems from linearly-expandable optical switching modules forany of the basic classes of optical switch architectures describedherein. The applications of the inventions to the architecturesdescribed herein are exemplary, and a person of ordinary skill in theart with the benefit of these teachings will be able to apply theinvention to other configurations of optical switch architectures.

In a first aspect, the invention pertains to an optical switching devicewith expansion connections comprising a photonic integrated circuit. Thephotonic integrated circuit can comprise N input optical ports whereN>1, an input light-path associated with each input port, M opticaloutput ports where M≧1, an output light-path associated with each outputport, a bypass optical switch block associated with each output port, Pexpansion-in ports where P≧1, an expansion light-path associated witheach expansion-in port and connecting with an associated bypass switchblock, a plurality of optical switching elements and associatedlight-paths forming a network of connections between the inputlight-paths and a by-pass switch block associated with an outputlight-path.

In a further aspect, the invention pertains to an optical switchingdevice with expansion connections comprising a photonic integratedcircuit. The photonic integrated circuit can comprise N input opticalports where N≧1, an input light path associated with each input port, Moptical output ports where M>1, an output light path associated witheach output port, a bypass optical switch block associated with eachinput port, Q expansion-out ports where Q≧1, an expansion light pathassociated with each expansion-out port and connecting with anassociated bypass switch block, a plurality of optical switchingelements and associated light paths forming a network of connectionsbetween the by-pass switch block associated with an input light path andthe output ports.

In additional aspects, the invention pertains to an expandable opticalswitch device for dynamically configuring the interconnections between aselected number of optical input ports and M optical output ports. Theswitch device can comprise Z optical switching modules (Z≧2) withoptical inter-connections to form a configuration having an initialmodule, a terminal module and optional intermediate modules, eachoptical switching module L comprising N_(L) input ports and M outputports and desired switching capability between the input ports andoutput ports with the sum of N_(L) equal to the selected number of inputports. Each optical switching module that is not an initial module canhave a set of expansion in ports coupled through bypass switches torespective output ports, and each optical module that is not a terminalmodule can have a set of output ports coupled to expansion in ports ofanother module.

In other aspects, the invention pertains to an expandable optical switchdevice for dynamically configuring the interconnections between Noptical input ports and a selected number of optical output ports, inwhich the switch device comprises Z optical switching modules (Z≧2) withoptical inter-connections to form a configuration having an initialmodule, a terminal module and optional intermediate modules. Eachoptical switching module L can comprise N input ports and M_(L) outputports and desired switching capability between the input ports andoutput ports with the sum of M_(L) equal to the selected number ofoutput ports. Each optical switching module that is not a terminalmodule can have a set of expansion out ports coupled through bypassswitches to respective input ports, and each optical module that is notan initial module can have a set of input ports coupled to expansion outports of another module.

Moreover, the invention pertains to an optical ring network comprising aplurality of nodes, two distinct optical rings connected to the nodes,and optical branches at each node providing an optical connectionbetween each optical ring and to N output optical lines wherein theoptical branches comprise two 1×N optical switches who each 1×N opticalswitch connected to a respective ring and N 2×1 bypass switchesconnecting the respective 1×N optical switches and the N optical lines.

Furthermore, the invention pertains to an optical network switching nodecomprising N optical light-paths, an N′×M′ cross connect switch (OXC),and an N″×M″ multicast switch (MCS), a set of bypass switches and a setof bypass light-paths between an OXC output and a bypass switch andwherein a bypass switch is also connected to an MCS output.

In further aspects, the invention pertains to an optical networkswitching node comprising N input light-paths, a drop bank and acontention mitigation structure, wherein the drop bank comprises amulticast switch (MCS) and the contention mitigation structure comprisesa selective optical switch with the output from the selective opticalswitch directed through light channels to inputs of the MCS, wherein theN input light paths are divided into a subset providing input to thecontention mitigation structure and a further subset providing input tothe drop bank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an optical switch having N inputs and M outputs;

FIG. 2 depicts a switch assembly having at least one switch equippedwith expansion ports;

FIG. 3 depicts an alternative embodiment of a switch assembly having atleast one switch equipped with expansion ports;

FIG. 4 depicts four modules interconnected to provide an N×M switch;

FIG. 5 depicts an expandable switching module;

FIG. 6 depicts an expandable switch that has a plurality of bypasslines;

FIG. 7 depicts a group of expandable switches assembled together;

FIG. 8 depicts an expandable multicast switch;

FIG. 9 depicts as assembly of expandable multicast switches;

FIG. 10 depicts a subsection of the switch of FIG. 8;

FIG. 11 is alternative expandable 4×1 circuit for a multicast switch;

FIG. 12 is another alternative expandable 4×1 circuit for a multicastswitch;

FIG. 13 is a conceptual arrangement of as expandable 4×3 planarlightwave circuit (PLC) cross connect;

FIG. 14 is an embodiment of a layout tor an expandable PLC;

FIG. 15 is a functional diagram of an expandable switch;

FIG. 16 is a functional diagram of optical modules of the switch of FIG.15;

FIG. 17 is a functional diagram of connections of the modules of theswitch FIG. 15;

FIG. 18A is a perspective view of a model of a front side of a card;

FIG. 18B is a perspective view of fee back side of the card of FIG. 18A;

FIG. 19 is a plan view of a subassembly of the card of FIG. 18A;

FIG. 20 is a perspective view of a subassembly of the card of FIG. 18A;

FIG. 21 is a perspective view of a subassembly of the card of FIG. 18A;

FIG. 22 is a perspective view of a subassembly of the card of FIG. 18A;

FIG. 23 is a top view of a layout for the expandable switch of the cardof FIG. 18A;

FIG. 24 a is an embodiment of a multicast switch;

FIG. 24 b is an alternative embodiment of a multicast switch;

FIG. 25 is a graph of received optical power at a CR;

FIG. 26 is an embodiment of a multicast ROADM with a crossover switchload balancer;

FIG. 27 is a bar graph of a ROADM coat using different multicast switchtypes and drop ratios;

FIG. 28 depicts an improved architecture for a ROADM using 8programmable splitters.

FIG. 29 depicts an MZI-basad programmable splitter and exemplaryspecifications;

FIG. 30 depicts an MCS with for the case wherein initial traffic flow isfrom only one direction;

FIG. 31 depicts an MCS with for the case wherein initial traffic flow isuniformly from all directions;

FIG. 32 depicts an MCS with for the case wherein fully automaticflexibility is provided;

FIG. 33 is a schematic of various hardware contention mitigationoptions;

FIG. 34 is a schematic of CD architecture with contention migration;

FIG. 35 is a conceptual diagram of a ring network with parallel opticalpaths connecting a set of nodes; and

FIG. 36 depicts an example of a node structure.

DETAILED DESCRIPTION OF THE INVENTION

Scalable optical switch modules provide for optical switching functionsfor optical networks, which can comprise large numbers of opticalpathways. A switch module can comprise an array of actuatable 1:2optical switch elements, 2:2 optical switches, splitters, and combiners,and can provide for connections to three sets of optical lines forintegration capability in one dimension or connections to four sets ofoptical lines for integration capability in two dimensions. The twobasic dimensions defining the switching function involve the inputoptical lines and the output optical lines. In some embodiments, anoptical switching module can have bypass switches to provide for thebypass of a string of optical circuit elements to reduce correspondingoptical loss from transmission through the switch elements if noswitching function is performed for a particular input/output linewithin a module upon integration into an array of modules. With theavailability of optical switch modules with reduced loss, a networkarchitecture can be designed that can take greater advantage of thescalable optical switching function. Thus, based on the use of scalableoptical switches, simpler scaling of optical network architectures maybe achieved. Based on the ability to perform large scale opticalswitching using purely optical switches, the number of optical toelectrical transducers within the network can be significantly reducedwhich results in a significant decrease in capital expenses as well assignificant decrease in power consumption. The expandable switches canbe conveniently constructed in the form of a placer light circuit,although the designs can also effectively be constructed from free spacecomponents, such as 1×2 or 2×2 switches connected with optical fibers.The expandable switches can be conveniently constructed in the term of aplanar light circuit although the designs can also effectively beconstructed from free space components, such as 1×2 or 2×2 switchesconnected with optical fibers.

As with all communication networks, optical networks integrate switchingfunctions to provide for various connections to provide for routing oftransmissions. For example, longer range transmission pathways areconnected with branches to direct optical signals between ultimatepathways associated with the sender and recipient. Separation ofparticular communications or portions thereof can be based on wavelengthand/or temporal differentiation within a combined transmission sent overlonger range trunk, i.e., combined signal, lines. At some location on anetwork, an optical band can be split to isolate specific signals withinthe band for routing, and similarly individual communications arecombined for transmission over combined signal lines. The opticalswitching function can be performed using electronic switching by firstconverting the optical signal into an electronic signal with appropriatereceiver(s). However, cost ultimately can be significantly reduced,and/or switching capacity significantly increased, if an efficientoptical switching can be performed with reduced conversion of opticalsignals into electronic signals. The optical switching modules describedherein provide desirable scalability through providing opticalconnections along multiple dimensions of a planar optical circuit alongwith an array of optical circuit elements.

If the optical switching cannot be appropriately scaled, opticalswitching can only be used in limited network architectures. Thus, amesh optical network has been described to provide switchingfunctionality based on 4-degree switching nodes. See, Prasanna et al.,“Versatility of a Colorless and Directionless WSS Based ROADMArchitecture,” COMSNET 2009 Conference, January 2009, Bangalore, India,incorporated herein by reference. Planar optical circuits have beendesigned to accommodate 16×16 optical matrix switching on a singlewafer. See, Goh et al., “Low Loss and High Extinction Ration StrictlyNon-Blocking 16×16 Thermooptical Matrix Switch on a 6-in Wafer UsingSilica-Based Planar Lightwave Circuit Technology,” J. of LightwaveTechnology, 19(3), pp 371-379 (March 2001), incorporated herein byreference. However, the design of the 16×16 optical switches describedby Goh et al. does not provide any straightforward scaling. Opticalswitching circuits described herein provide a high degree of scalabilitythrough the introduction of an additional layer of connectivity withinthe circuit, in which each individual optical circuit provides an n×marray of switches. The n×m array can be associated with n input opticalports and m output optical ports. The switching function can bereferenced to N input lines and M output lines to provide for desiredswitching within the network, and the N×M switching function can beaccomplished through the appropriate integration of the n×m switchingfunction of the individual modules.

Optical and electronic switching complement each other in a switchingnode. Though improvements are still coming, the basic character ofelectronic switching is well established. The technology for opticalswitching however is still emerging and various innovations are stillneeded for optical switching devices to begin to fully address theirexpected domain. Present and forthcoming optical switching systemsgenerally fall into a few basic architecture classes. Though there arenot firm, universally accepted boundaries between these classes,generally they are thus: basic reconfigurable optical add-dropmultiplexer (ROADM); wavelength-selective switch (WSS); opticalcross-connect (OXC, or less commonly OCX); simple branching (1×N, N×1);and multicast switch (MCS). The fundamental operating characteristicsfor each of these classes are well established.

In summary, a basic ROADM provides the capability to independentlydetermine for each wavelength in an input fiber whether that wavelengthwill be routed to the corresponding output fiber or dropped to a localport or different fiber pair. Additionally in a basic ROADM, anywavelength that is dropped and thus not directly routed to the outputcan be used to introduce new optical data streams from the local portsor other fiber pair into the output fiber. It is an unfortunatecircumstance of optical networking arts that there are two verydifferent items that bear the designation ‘ROADM’. The ROADM componentis as described in the preceding, but there are also higher-degree ROADMsystems that can be used to selectively drop or route through individualwavelengths among a larger number of input/output fiber pairs.Originally ROADM systems were simply collections of ROADM components andthe control systems that tied them together and the common namepresented no problem. These higher-order ROADM have, however, evolvedand often comprise some of the other classes of optical switchesincluding, for example, WSS, OXC and MCS. Legacy ROADM components stillexist, but the ROADM term more commonly now refers to the higher-ordersystem. Subsequently the term ROADM, unless specifically citing ‘ROADMcomponent’, shall refer to the higher-level ROADM system. Specificembodiments are presented below of expandable OXC and MCS along withROADM incorporating expandable MCS.

Current WSS class switches have a single input and several outputs andeach wavelength on the input can be independently routed to any of theoutputs and each output can accommodate any number of the wavelengths onthe input fiber. The WSS, like most classes of transparent opticalswitches, provides a connection between the input and output equallywell for optical signals propagating from the input to an output, orpropagating from the same output to the input. Therefore, the terms‘input’ and ‘output’ are used merely as a convenience to describe theoperation principle, but in practice they may be used as described ormay be used in the reverse direction. There is also presently muchconsideration of a future WSS-class switch where a single component canroute wavelengths among multiple inputs and multiple outputs, but as ofyet it is only practical to provide such a capability as a higher-levelsystem using multiple discrete components.

The OXC provides arbitrary permutation of a sequence of input portsamong a usually equal number of output ports, although more generally adifferent number of output ports, as described below. This can forinstance transform a set of input ports where each port carries only onespecific wavelength from one specific fiber as a set of output portswhere each output port can be programmed to carry any wavelength fromany fiber. A simple branching switch provides basic 1×M switching whereall the optical signals in the single input port are routed together toone of the N output ports. This switch is also reversible wherein Nseparate optical signals some into the N ports and the switch selectsthe signals form just one of those ports to be routed to the single‘input’ port operating as an output.

A M×N multicast switch uses M 1×N splitters at the M input channels todistribute all the optical signals in each input port towards each ofthe M outputs. Each of the N outputs has its owe M×1 selector switch toisolate the signals from the desired input port. The MCS has the basicadvantage of having no optical filtering, so it is not only transparentto the data in each wavelength, it is transparent to the wavelength setconfiguration itself (“colorless”), i.e., wavelength channels do notneed to conform to any specific wavelength grid specifications orchannel bandwidths. The primary cost of this added transparency is thereduction of signal power due to the optical splitting on the inputstages, and the MCS in some applications involves an array of opticalamplifiers to boost the signal level and compensate the additional lossfor each input.

Optical nodes in a communication network can comprise one or more ofoptical switching components from one or more of these classes. Asnetworks become larger and more complex, scalability can be asignificant issue generally and is particularly significant with respectto switching capability. Desirable optical nodes are constructed to becolorless, directionless and contentionless, as described furthersubsequently. It is the nature of these networks that there issignificant variation in the nominally best configuration for each ofthose nodes. The present state of the art for optical switchingcomponents is such that each product tends to support a specific portcount, realizing a similar component providing a different port countrequires a separate product development. This discourages thediversification that would most appropriately address the needs of avariety of optical nodes and forces node design towards a lessefficient, one-size-fits-all approach. There is a clear and present needfor a means to more flexibly adapt the size of optical switchingmatrices using any one or more of the basic optical switching classes.The expandable switches described herein provide an important andinnovative component the adaptable node design.

The optical switching function described herein can be sealed throughthe integration of the individual switching modules into an effectivelarger switching array assembled from individual optical circuitmodules. The integration of the modules to provide the scalability canbe performed in one dimension or two dimensions. To perform theintegration in one dimension, the optical circuit can be designed withan additional set of ports corresponding either to the n input opticalports to form an effective expanded array with dimensions (b·n)×mswitching or to the m output optical ports to form an effective expandedarray with dimensions n×(c·m) switching. The parameter b is the numberof n×m optical circuits that are interconnected with respect to theinput lines to form the expanded switching array; and similarlyparameter c is the number of n×m optical circuits that ateinterconnected with respect to the output lines to form the expandedswitching array. With respect to optical integration in two dimensions,the optical circuit modules are formed with 4 sets of optical ports,with two sets of n ports and two sets of m ports. These optical circuitscan then be assembled into an expended array with (b·n)×(c·m) switchingcapability. Parameter n may equal but does not necessarily equalparameter m.

The individual optical circuits can comprise an array of (2×2 or 2×1)optical switches connecting n inputs with m outputs. Each 2×2 (or 2×1)optical switch provides an actuatable switch between an input line andan output line. Suitable actuatable optical switches are describedfurther below, and generally the actuatable optical switched arecontrolled electronically to toggle the switch between interconnectionconfigurations. With the array of actuatable optical switches in amodule, a signal associated with one of the n input ports can be routedto one of the m output ports through the passage through the array ofactuatable optical switches. The integration with another opticalcircuit through the connection of another set of n ports to the inputports of the second optical circuit provides access to a second array ofn×m (2×2 or 2×1) optical switches so that effectively another m outputports can be accessed in the integrated expanded array. The integrationcan be continued. Similarly, the integration with another opticalcircuit through an additional set of m ports can provide access of the moutput ports to a second set of n input ports in the integrated expandedarray. Continuing the integration can lead to the (b·n×c·m) scalabilityin which parameters b, c, or both b and c b greater than 1. In theintegrated expanded array there is an effective array of actuatableoptical switches connecting b·n inputs with c·m outputs. Thus, theexpandable optical circuits designs provide for great scalabilitycapabilities. To match the sealing of the optical circuit modules withthe targeted network switching function, generally (b−1)·n<N≦b·n and(c−1)·m<M≦c·m, where N is the network inputs and M is the networkoutputs. Analogous reasoning can show that the numbers ‘n’ and ‘m’ donot need to be the same among all the components of the expanded arrayproviding even greater flexibility over achievable configurations.

Any reasonable design of an actuatable optical switching element can beassembled into the array, as described further below. While opticalcircuit designed for the switching devices with an additional set or twosets of optical ports provide very desirable scaling capabilities, thepassage of signals through the expanded array of 2×2 or 2×1 apnealswitches can result in an undesirable level of optical loss.Specifically, passage of an optical signal through the actuatableoptical switches generally masks in some optical loss even if the switchis in the “through” or non-switching mode. In the scaled integratedswitch, an optical signal can pass through a significant number ofactuatable switches even if switching is only performed at one of theactuatable optical switches. Thus, in some embodiments, the planaroptical circuits or other expandable switch designs comprise bypassoptical pathways that provide the capability to bypass a set ofactuatable optical switches to reduce corresponding loss if a particularinput or output line does not undergo any switching within theparticular module at that time. Control of the direction of an opticalsignal alternatively along the bypass pathway or the switched pathwaycan be itself controlled with a single 1×2 optical switch. Bypasscapability can be established for input lines, output lines or both.

In the description of the topology of the layout of the actuatableswitches, the term array is used in its general sense and notnecessarily directed to a matrix lay out. Two specific embodiments aredescribed in more detail below. An embodiment of an expandable crossconnect switch has a matrix of 2×2 switches in the logical ortopological layout of the cress connect n×m expandable switch. Inanother embodiment an expandable multicast switch is described with abranching layout of splitters that meet an array of 2×1 switches tocouple the expanded n×m split inputs into the m outputs in which thearray of switches are not arranged in a matrix configuration. Of course,the physical layout of the actual devices generally does not resemblethe topological layout of the devices due to the aspect ratios, packing,and other practical considerations.

The scalable optical switch can be designed for integration into acolorless, directionless, and contentionless (CDC) network node. Thereference to colorless refers to the ability to drop or add a particularlight wavelength at any port. The reference to directionless refers tothe ability to connect to all directions from local transponders, whereeach ‘direction’ directly corresponds to a particular inbound/outboundfiber pair connecting to the node. The reference to contentionlessindicates that the node can resolve the problem of two distinct opticalsignals converging on the node on different fibers but containing thesame wavelength and bound for a common optical pathway. This is commonlyresolved by rerouting one of the wavelengths to local traffic where itcan be electronically switched to another available wavelength andre-inserted into the desired pathway generally connected to an outboundfiber. The scalable switch device described herein generally satisfiesthese features and can correspondingly be integrated into a CDC networknode.

The schematic view of an N×M optical switching cross-connect (OXC)within an optical network is shown schematically in FIG. 1. N×M opticalswitch 100 is optically connected to N input optical lines 102, e.g.,optical fibers, and M output lines 104, e.g., optical fibers. N, thenumber of input lines, may or may not equal M, the number of outputlines. Due to the scalability of the optical switching function asdescribed herein, N and M generally can be relatively large, and inembodiments of particular interest N and M are independently each atleast about 8, in further embodiments at least about 16, and in otherembodiments at least about 32 or larger or intermediate even or oddinteger value. Similar comments on ranges of input and output linesapply to other switching embodiments described herein. A person orordinary skill in the art will recognize that additional ranges ofoptical lines within the explicit ranges above are contemplated and arewithin the present disclosure.

In general, the optical switching device can be placed at any convenientlocation within an optical network. From that perspective, signalstransmitted within the individual input lines and output lines may ormay not be intended to carry individual communications, and these can becombined signals carried within a band of wavelengths. In someembodiments, the optical switches are associated with MUX/DeMUXcapabilities to split and/or combine optical signals within an opticalband. The expressions MUX and deMUX are used herein respectively formultiplexing and demultiplexing functions, as is generally accepted inthe art. MUX and DeMUX functions can be performed with planar ArrayedWaveguide Gratings (AWG) or other desirable dispersive elements. In someembodiments, the input signals can comprise signals intended for a setof users, and the output lines represent optical branches directed to aspecific user, which corresponds to use of the switching element at theend of an optical network for directing signals to end users. The inputand output designations can be arbitrary in the sense that signals canbe directed through the switch in either direction, such that theswitching function is optically reversible. But the input and outputdesignations are used to describe groupings of optical lines that arerouted between each other regardless of the direction of thetransmissions. In other embodiments, the switch can be used to directmultiplexed or combined signals at a branch along an optical networkaway from any users.

Although this invention can be employed to improve various means ofoptical switching, the scalable optical switches as described herein areexemplary of an assembly of optical circuits. The optical circuits arecorrespondingly designed with appropriate connectivity to provide thescalability. The optical circuits are interconnected as modules toprovide the desired level of optical switching. The invention can beparticularly advantageous when the optical circuits are integrated asplanar optical circuits.

The interconnection of two optical circuits to provide scaling withrespect to input lines is shown schematically in FIG. 2 in a conceptualframework that is expanded upon in detail in the context of somespecific embodiments. Optical switching functions are accomplished, forinstance, by assembly 108 having a first switch 109 having opticalcircuit 110 and second switch 111 having optical element 112. Circuit110 composes N input ports 107, M output ports 121 and M expansion-inports 123. Similarly, circuit 112 comprises N input ports 118 and Moutput ports 120. Circuits 110, 112 are interconnected with Mexpansion-in ports of first switch 109 being connected with M outputports of second switch 111 through optical interconnections 114, such asoptical fibers or other suitable optical connections, N₁ input opticallines 116 are connected to planar optical circuit 110, and N₂ inputoptical lines 117 are connected to planar optical circuit 112. M ports121 of circuit 110 have output lines 125. Thus, together assembly 108 ofoptical circuits 110, 112 provides switching between N₁+N₂ input portsand M outputs. This schematic diagram demonstrates a case where thenumber of total inputs (N₁+N₂) is greater than the total number ofswitched outputs. This embodiment demonstrates how expansion-in portscan be used to effectively expand a number of inputs with specific sizedswitches available that may individually have lower capacity. Forinstance, the use of a switch with expansion ports in the assemblychanged a 4×6 switch into an 8×6 switch, which doubled the number ofswitched inputs.

Scalability with respect in output lines is shown schematically in FIG.3. In the embodiment of FIG. 3, optical switching is provided byassembly 127 having an integration of switches 128 and 129. Switch 128comprises optical circuit 130. Switch 129 comprises optical circuit 132.Circuit 130 comprises N input ports 134, M output ports 136, and Mexpansion-out ports 138. Similarly, circuit 132 comprises N input port140 and M output ports 142. Circuits 130, 132 are interconnected withexpansion-out ports 138 to inputs 140 through optical interconnections144. N₂ optical input rises 146 and M2 optical output lines 148 are alsoconnected to circuit 130. M1 output lines 150 are further connected tocircuit 132. This embodiment demonstrates a case where the number oftotal outputs (M₁×M₂) is greater than the total number of inputs (N₁ orN₂), although alternative embodiments may involve a greater number ofinputs relative to outputs or equal numbers. This embodiment alsodemonstrates how expansion-out ports can be used to expand an effectivenumber of outputs. Specifically, use of a switch with expansion portswas used to change a 4×6 switch into a 4×12 switch, which doubled thenumber of switched outputs.

FIG. 4 depicts the connection of four modules 149, 151, 153, 155 each,comprising a optical circuit that provides scalability with respect toboth input lines and output lines. The switching function is provided byoptical circuits 150, 152, 154, 150. Optical circuit 150, such as aoptical circuit, is optically connected with a number N₁ connections tooptical circuit 152 and with a number M₁ connections to optical circuit154. The numbers N₁ and M₁ vary from N_(1i) to N_(1t) and M_(1i) toM_(1t), respectively. Optical circuit 154 is optically connected with N₂connections to optical circuit 156, and optical circuit 152 is opticallyconnected with M₂ connections to optical circuit 156. The numbers N₂ andM₂ vary from N_(2i) to N_(2t) and M_(2i) to M_(2t), respectively. If Nis the total number of user input connections, then N₁+N₂=N, or N₁+N₂ isgreater than N if the integrated modules have excess unused capacity.Similarly, if M is the total number of output connections, M₁+M₂=M, orM₁+M₂ is greater than M if the integrated modules have excess and unusedcapacity. Optical circuit 150 provides optical switching between N₁input lines and M₁ optical output lines, and optical circuit 152provides optical switching between N₁ optical input lines and M₂ opticaloutput lines. Correspondingly, optical circuit 154 provides opticalswitching between N₂ input lines and M₁ optical output lines, and planaroptical circuit 156 provides optical switching between N₂ optical inputlines and M₂ optical output lines. Thus, together optical circuits 150,152, 154, 156, which can be planar optical circuits, provide switchingbetween N input optical pathways with M output optical pathways. Thescalable aspect of interconnection of the modules provides that N and Mmay be independently chosen, e.g., N=M, N>M, or N<M. While FIG. 4depicts 4 expandable optical circuits, the expansion ability providesthat additional optical circuits can be correspondingly interconnectedto further increase input capability, output capability or both inputand output capability.

FIGS. 2-4 schematically show scalability of optical switching within thecontext of optical switch 100 of FIG. 1. In particular, planar opticalswitches are designed for integration as modules to accommodateexpansion with respect to the member of input lines and/or the number ofoutput lines. While FIGS. 2-4 are directed to disclosing the integrationwith respect to two modules in the input dimension and/or two modules inthe output dimension, the scalability can be similarly extended in theinput dimensions and/or the output dimension to include greater than twoswitching modules in each dimension, such as three modules, four modulesand so on. With respect to FIGS. 2-4, the individual switching modulehas been depicted schematically.

An example of a switching module is an army of optical switches. Inthese embodiments, the switching modules each generally comprise an n×marmy of (2×2) actuatable optical switches that provide for optionalswitching from an input optical line to an output optical line. FIG. 5depicts switching module 502 having four input channels 504 a, 504 b,504 e, 504 d; four downstream expansion-out channels 506 a, 506 b, 506c, and 506 d; and three drop ports 508 a, 508 b, and 508 c. Inputchannels 504 a, 504 b, 504 c, and 504 d are connected to downstreamexpansion-out channels 506 a, 506 b, 506 c, and 506 d by paths 510 a,510 b, 510 c, and 510 d, respectively. Each of input channels 504 a, 504b, 504 c, and 504 d are switchably connected by paths 512 a, 512 b, and512 c to each of drop ports 508 a, 508 b, and 508 c. Cross-pointswitches 516 are located at the points where paths 510 a, 510 b, 510 c,and 510 d cross paths 512 a, 512 b, and 512 c.

Operation of the basic switch matrix is straightforward. Cross-pointswitches 510 can be designed to normally allow the optical paths tocross each other unaffected, and the majority of the switches in thematrix may be in this state for any given configuration. When aparticular input channel 504 a, 504 b, 504 c, or 504 d is selected to berouted to a particular drop port 508 a, 508 b, or 508 c, a switch 516 atthe single crossover point for those two waveguides is activated toreroute the input channel. For any valid configuration tor a crossconnect switch, no more than one switch in any row or in any column isin a fully switched state, as shown in FIG. 5. When the switch is in theswitched state, a signal from the input far that drop port is alsorerouted to the downstream portion of that input channel, sofunctionally the device can perform both add and drop at the same time.This behavior could be provided by most any optical switching solution,out it rarely if ever is, so it is presumably generally not desired.This behavior can also support certain other functions in more complexswitching assemblies.

In same embodiments, so expandable switch has a plurality of bypasslines. One advantage of a bypass line is that a signal can bypassswitch/junctions to reduce signal less. One embodiment of a bypass lineprovides that 1×2 (or 2×1) bypass switches are placed on input linesand/or drop lines to provide for bypass of a circuit for when noswitching takes place for the particular line in the particular circuit.For planar optical circuits, arrays of bypass 1×2 optical switches canbe placed on the same optical circuit chip as the N×M expandable switchor on a separate optical circuit chip. If the intended Drop port forthat input channel is on the present module, the signal will be routedto the row of switches as usual. If not, the signal channel will berouted through a bypass channel past all the switches to the ExpansionOut port. Likewise, each Drop port can be connected through a 2×1switch. If the input channel intended for that Drop port is on thepresent module, the 2×1 switch will select the waveguide coming from thecolumn of crosspoint switches for that port. If not, it will select achannel coming from the Expansion In port bypassing the column ofcrosspoint switches.

An embodiment of an expandable switch that has a plurality of bypasslines is depicted in FIG. 6. Expandable switch 600 comprises array 602of optical cross-point switches 604 placed at the cross points of inputchannel selectable lines 606 and drop lines 608. In the depictedembodiment, channel selectable lines 605 and drop lines 608 pass througha plurality of cross-point switches 604 which have a position forallowing signals in selectable lines 606 and/or drop lines 608 to passunswitched therethrough. One or more bypass lines may be provided forone or more channel line and/or one or more drop line. In FIG. 6, thereare channel bypass lines 610 and drop bypass lines 612. Input 1×2switches 614 provide for input lines 615 to be connected to switch 614so that switch 614 is operable to switch light from input lines 615 to achannel bypass line 610 or a channel selectable line 606. Drop 2×1switches 618 allow for either a drop line 608 or a drop bypass line 612to be selected and passed to output lines 617. Alternatively, switchesmay be provided that have continuous adjustability such that a switchcan direct the input signal in a limits to select none or both lines.Bypass lines are connectable at an expansion port at one end and areconnected to a bypass switch at the other. Channel bypass lines 606 haveconnectivity at Expansion-output ports 620 or other connectivity deviceis provided for connection to another expandable switch or some otherdevice. Drop bypass lines 612 have connectivity to receive input atExpansion-input ports 622. In use, one or more expandable switches 600are connected with Expansion-output ports 620 optically communicatingwith input lines 615 and/or output lines 617 optically communicatingwith Expansion-input lines 622. After assembly of a plurality ofexpandable switches, a signal that enters a switch 614 is routed to adrop-port if the desired drop-port is on the switch or is passed via abypass line to another switch. A designation as an input line versus adrop line is arbitrary for devices with switches that pass light ineither direction: accordingly, the input and drop lines may be reversed.To simplify the drawing, only a portion of equivalent components arelabeled with reference members.

FIG. 7 depicts a group of expandable switches assembled together. Switchassembly 700 has expandable switch modules 720, 740, 760, 780.Expandable switch modules 720, 740, 760, 780 comprise arrays 722, 742,762, 782 of optical cross-point switches 724, 744, 764, 784 placed atthe cross points of input channel selectable lines 726, 746, 766, 786and drop lines 728, 748, 768, 788, channel bypass lines 730, 750, 770,790 and drop bypass lines 732, 752, 772, 792. Input 1×2 switches 733,753, 773, 793 are connected to switch light signals from inner lines734, 754, 774, 774 to a channel bypass line 730, 750, 770, 790 or achannel selectable lines 726, 746, 766, 786. Drop 2×1 switches 735, 755,775, 795 allow for either a drop line 728, 748, 768, 788, or a dropbypass line lines 732, 752, 772, 792 to be selected and passed to outputlines 736, 756, 776, 796. Alternatively, switches may be provided thatprovide continuous range switching function.

Channel bypass lines 730, 770 are optically connected to loom lines 754,794, respectively. Drop 2×1 switches 735, 755 are optically connected topass signals to drop bypass lines 772, 792. Ports (schematically shownas edges of for switches intersecting optical paths) are provided forconnection to user devices and/or to other expandable modules. The termuser devices is a broad term that encompasses networks, subnetworks,nodes, specific devices, network communications devices, and end-userdevices. Inlet ports provide optical connections to input lines 734,754, 774, 794; in this embodiment lines 734 and 774 are available forconnection to user devices and pores for input lines 774 and 794 areconnected to other expansion modules. Expansion-input ports provideoptical connectability to drop bypass lines 732, 752, 772, 792; in thisembodiment, lines 732 are dormant and lines 772 are available forreceiving optical signals from expansion-in ports to provide fordirecting signals from inputs 734 to outputs 776. Expansion output portsprovide optical connectability to channel bypass lines 730, 750, 770,790; in this embodiment, lines 750 and 790 are dormant and ports forlines 730 and 770 are connected through expansion out ports to inputports of switches 740 and 780, respectively.

In the actual chip layout, the switches on the In port add one stage andthe switches on the Drop port also add one stage. In this way, largerswitch matrices can be arbitrarily (at least in terms of functionalgeometry) scaled up from a single common module.

Also consider that 1×2 switches could be integrated on the Expansion Outterminals of the switch module to enable each module to connect to twodownstream drop modules and likewise the Expansion In terminals couldhave 2×1 switches and thus each module could forward drop channels fromtwo additional channel beams. This would allow matrices to be built upfrom a single module type along the branches of a tree geometry ratherthan sequential layout, likely improving overall optical efficiency.Also, the switches on the Expansion ports would overlap the switches onthe In and Drop ports and hence would not add any stages to the physicallayout in planar integrated module, hence imposing very little increasein the size of the planar chip.

FIG. 8 depicts an embodiment of an expandable multicast switch.Components of the switch are arranged to illustrate theirinterconnections and how paths, switches, and splitters can be made tocooperate to provide expandability in a multicast application. Artisansreviewing this illustration will be able to make physical device layoutsas described further below. Expandable multicast switch 800 has splittertree 802 and switching section 804. Splitter tree 802 multiplies opticalinputs a, b, c, d so that each one is connected to each optical outputline X1-X8. Input ports (not shown) are provided to provide opticalconnections from the device interface to inputs a-d. Splitter tree 802has three levels to appropriately spilt the signal, into appropriatenumber of optical paths, although a different number of levels can beused depending on the number of input lines and desired multicastinginto particular output optical lines. Level 1 has an optical splitter oneach input, with splitters 811 a, 811 b, 812 c, 811 b splitting inputlines a, b c, d, respectively to thereby make 2 branches tor each input,for a total of 8 branches. The split signals are passed to level 2splitters 821 a, 821 b, 821 c, 821 a, 822 a, 822 b, 822 c, 822 a thatsplit the signals into 2 branches for each input to that level, for atotal of 16 branches and a total of 4 signals for each of inputs a-d.The split signals are then passed to level 3 splitters 831 a, 831 b, 831c, 831 d, 831 a′, 831 b′, 831 c′, 831 d′, 832 a, 832 b, 832 c, 832 d,832 a′, 832 b′, 832 c′, 832 d, 833 a, 833 b, 833 c, 833 d, 833 a′, 833b′, 833 c′, 833 d, 834 a, 834 b, 834 c, 834 d, 834 a′, 834 b′, 834 c′,831 d+, that each spin the signals into 2 branches thereby making 32branches and a total of 8 signals for each of inputs a-d. Switchingsection 804 has Expansion-in ports (schematically shown as the end ofcorresponding optical paths) connected to bypass lines 806 labeled,which are connected to bypass switches as noted below. Output lines 808labeled X1-X8 each optically connected to an Output port (schematicallyshown as the end of the output lines). Switching blocks 841, 841′, 842,842′, 843, 843′, 844, 844′ provided switchable connections from splittertree 802 to the output lines 808. Each switching block connects inputsa-d to a bypass switch 851, 851′, 852, 852′, 853, 853′, 854, 854′ thatare optically connected to switch between the signal from splitter tree802 of a bypass line 806 for passage to output line 808. Specificallyfor block 841, for instance, optical switch 841 ab provides for input aor b to be chosen, with the chosen signal a/b being passed to switch 841bc that provides for switching between a/b or c, with the chosen signala/b/c being passed to switch 841 cd that provides for switching betweena/b/c and d. Switching block 841 then passes one of the signals a-d tobypass switch 851, which provides for a choice between a/b/c/d andbypass path 806 labeled B8. The signal selected by bypass switch 851then passes to output line 808 labeled X8. In use, one or moreexpandable switches may be connected with outputs labeled X1-X8 inoptical communication with expansion-in ports labeled B1-B8. Inputs a-dare available for switching so that any outlet X1-X8 can carry any oneof inputs a-d. Outlets X1-X8 can alternatively carry a signal receivedfrom expansion-in ports. In use, optical connections are made to one ormore expansion-in ports, to one or more input ports, and to one or moreoutlet ports. Signals passing into the input ports and/or expansion-inports are selected to pass out of any of outputs 808. Note also there isno restriction against bypass switches 851 providing continuous-rangeswitching to support applications where additional combining of inputsignals with expansion-in signals is desired.

While FIG. 8 is shown with specific numbers of input optical lines andoutput optical lines, other embodiments can be similarly designed withdifferent numbers of inputs and outputs. The splitter tree can becorrespondingly changed, and redundant split optical lines can be formedif a convenient splitter tree provides a greater number of optical linesthan the number of output lines. Redundant optical lines can be dormantand just guide any optical signal away from any interfering propagation.Alternative designs of switching blocks are described below.

FIG. 9 depicts assembly 900 of terminal expandable switch module 920 andinitial expandable switch module 910, each expandable switch modulebeing essentially of the embodiment described as FIG. 8. The outputs 913of initial module 910 are optically coupled to the correspondingexpansion-in ports 922 of terminal module 920 by means of light paths902. Expandable switch modules 910 and 920 may be for instanceindividual design cells on a common planar substrate in a photonicsintegrated circuit (PIC) and the interconnecting light paths 902 couldbe optical waveguides on the same substrate. In another example,expandable switch modules 910 and 920 may be for instance individuallypackaged switch modules based on separate PICs and interconnecting lightpaths could be single-mode optical fibers either as a set of individualstrands or as a fiber ribbon. Each output in output set 923 can beconfigured to selectively connect to one of the inputs 921 of terminalmodule 920 by setting the associated bypass switch in 924 a-g to connectto one of the local inputs as detailed in the description of FIG. 8.Alternatively, each output in output set 923 can be configured toselectively connect to one of the inputs 911 of initial module 910 bysetting the associated bypass switch in 914 a-g to connect to theassociated expansion-in port as detailed in the description of FIG. 8,then further setting the appropriate switch elements in switch module910 to connect the selected input from inputs 911 to the output inoutputs 913 that is connected to the corresponding expansion-in port inexpansion-in ports 922. Thereby, a 4×8 expandable MCS 920 can beupgraded by attaching a second 4×8 MCS 910 to the expansion-in ports 922forming an assembly 900 of two 4×8 switch modules that provides the samefunctionality as a dedicated 8×8 MCS.

FIG. 10 is an enlarged view of a subportion of FIG. 8 depictingswitching blocks 841, 841′ joining the splitting tree with bypassswitches. Arrows a, b, c, d, depicts inputs passed from level three ofthe splitting tree. In this embodiment, each switching block receives 1input from each of the four potentially available inputs a-d. Eachbypass switch provides a choice to output one of a-d or a signal in thebypass line. The switching blocks are arranged in a serial configurationto sequentially select between a signal from an added optical line.

FIG. 11 is an alternative subportion for an expandable switch. Switchingblocks 1102, 1104 are arranged in a tree configuration and are afunctionally-equivalent alternative to switching blocks 841 and 841′ ofFIG. 10. In block 1102, switch 1106 is selectable between a and b inputsto provide output a/b and switch 1108 is selectable between c and dinputs to provide output c/d. Switch 1110 is selectable between a/b andc/d to provide an output a/b/c/d to bypass switch 1112, which is, inturn selectable between a/b/c/d or bypass B1 signal. Switches 1114,1116, 1118, 1120 are similarly configured to provide selectivity betweenany of a-d and B2.

FIG. 12 is an alternative subportion for an expandable switch. Switchingblocks 1208, 1210 are arranged in a tree configuration and depict analternative distributed layout of switching blocks 1102 and 1104 in FIG.11. Switching block 1208 has switches 1210, 1211, 1212 that areassociated with bypass switch 1214. Switching block 1215 has switches1216, 1218, and 1220 that are associated with bypass switch 1222. Switch1210 is selectable between and b to pass a/b to switch 1212. Switch 1211is selectable between c and d to provide output c/d that is passed toswitch 1212, which, in turn selects between a/b and c/d. Associatedbypass switch 1214 is selectable between a/b/c/d and B1. Switching block1214 and associated bypass switch 1222 are similarly selectable todirect a/b/c/d/B2 to an output 1224.

A conceptual arrangement of an expandable 4×3 planar lightwave circuit(PLC) cross connect is shown in FIG. 13. Expandable 4×3 PLCcross-connect 1300 has N_(i) inputs 1302 and N_(e) expansion inputs1303. Switch 1300 has M_(o) outputs 1308 and M_(e) expansion outputs1309. Bypass switches 1312, 1314 serve inputs 1302 and 1301,respectively. A significant feature to note is that in a compactarrangement, the length of the waveguide array supports a series ofswitching stages where the number of stages is M+N+1. Based on currentfeature sizes, switches larger than 4×4 would involve wrapping thewaveguides on the PLC chip. An 8×8 PLC cross connect switch is describedin Goh et al., “Low Loss and High Extinction Ration Strictly Nonblocking16×16 Thermooptic Matrix Switch on a 6-in Wafer Using Silica BasedPlanar Lightwave Circuit Technology,” Journal of Lightwave Technology19(3):371-379 (March 2001). The rough layout of a PLC as describedherein that approximately follows a layout set forth in the Goh articleis shown in FIG. 14. Switch 1400 has inputs 1402 and outputs 1404, withswitching/interfering modules 1406 with labels #1 to #15. A set ofbypass switches 1408 is provided to switch inputs 1402 and outputbypasses 1410 are provided near outputs 1404. As described previously,in applying the present invention, to this type of physical layout, theexpansion waveguides and bypass switches of the present invention can berouted adjacent to the existing waveguides and switches, retaining theexisting staging, thereby imposing little or no increase to the requiredsize of tire integrated chip.

Multicast Switch (MCS) Design

A desirable MCS switch design has been developed that can beconveniently placed on two planar lightwave circuits that interfaceappropriately. Also, these MCS swash designs can be made expandablethrough the use of optionally either 1×2 switches or 1×2 opticalsplitters for each Add In or Drop In line. The switched or split signalsare directed to separate MCS switch systems. This provides forscalability on the output lines. Similarly, input lines can be scaled bysplitting the lines the input to separate MCS switch systems, and thencorresponding outputs from the different MCS switch systems can becoupled back together.

A desirable MCS design is shown in FIGS. 15-23. Scalability features areonly shown on FIG. 15 for simplicity. The design on these figures, forexample shows two optical multicast switch functions 1502 (eachconsisting of an array of optical splitters 1054, and array of opticalswitches 1506, and interconnection 1508 between the two), 32 optical tapcouplers 1510, 32 photodiodes 1512, 22 photodiodes, 32 optical isolators1514, 16 gain flattening filters 1516, 16-erbium-doped fiber spools1518, two 1×8 tunable splitters 1520, the interconnect between all ofthe above functions and the electrical control electronics.Switches/splitters 1522 (FIG. 15) may employed, with a plurality of MCS1500 being downstream of the same. In the embodiment shown in thefigures, the functions are efficiently partitioned into separate modules1530, 1540, 1550 with fiber interconnects 1552, 1552′ between them. Onemodule 1530 comprises planar lightwave circuits (PLC) based monolithicintegration of optical functions, a photodiode hybrid integration andthe electrical control. The second module 1540 comprises discretecomponents that are arrayed in such a way that allows efficient fiberinterconnection between the first module and the second module. Thirdmodule 1550 can comprise wavelength division multiplexer, e.g., anarrayed waveguide grating or the like, and tunable splitter (TSPL).FIGS. 18-23 show a depiction of various views of an embodiment ofassembled modules forming the device.

In general, the expandable switching elements shown schematically inFIGS. 1-13 can be effectively formed using free space optical componentsconnected with optical fibers. Suitable individual switches, opticalsplitters, optical fiber connectors and other incidental components arecommercially available and improved versions are under continuousdevelopment. However, it can be desirable to integrate the devices asplanar optical circuits on an appropriate chip. Thus, an expandableswitch can be formed as an individual planar device with appropriatepackaging, and suitable connectors can be used to connect multipleswitches to take advantage of the expansion capability. The layout ofthe large number of connections on a planer chip is an art to obtain anappropriately small foot print with all of the availablefunctionalities. An example of such a layout is shown in FIG. 23.

The materials for forming the PLC can be deposited on a substrate usingCVD, variations thereof, flame hyrolysis or other appropriate depositionapproach. Suitable substrates include, for example, materials withappropriate tolerance of higher processing temperatures, such assilicon, ceramics, such as silica or alumina, or the like. In someembodiments, suitable silicon dioxide precursors can be introduced, anda silica glass can be doped to provide a desired index of refraction andprocessing properties. The patterning can be performed withphotolithography or other suitable patterning technique. For example,the formation of a silica glass doped with Ge, P and B based as plasmaenhanced CVD (PECVD) for use as a top cladding layer for a PLC isdescribed in U.S. Pat. No. 7,160,746 to Zhong et al., emitted “GEBPSGTop Clad for a Planar Lightwave Circuit,” incorporated herein byreference. Similarly, the formation of a core for the optical phasewaveguides is described, for example, in U.S. Pat. No. 6,615,615 toZhang et al., entitled “GEPSG Core for a Planar Lightwave Circuit,”incorporated herein by reference. The parameters for formation of anappropriate waveguide array are known in the art. Similar processing canbe performed using InP glass or other optical glass materials.

In general, optical signals passing through a switch can have attenuatedsignals. While the expansion designs herein can reduce such attenuation,it can be desirable to associate the expandable switches withappropriate optical amplifiers. Thus, it can be desirable to layer anarray of optical amplifiers coupled into the inputs of the switch,although the precise structure can be designed appropriate to thesystem. In particular, some structures are described below in thecontext of a ROADM.

ROADM Architecture with Multicast Switch

A desirable colorless, directionless, contentionless, and flexible-gridROADM architecture is based on a M×N multicast switch and a OXC loadbalancer. Multi-degree colorless and directionless ROADMs based on abroadcast (via 1×N optical couplers) and select (via M×1 wavelengthselective switches (WSS's)) architecture in express paths have beendeployed for several years [1,2]. However, with respect to localadd/drop paths, so far only colored wavelengths (λ's), or a limitednumber of colorless λ's have been deployed. Owing to the last trafficgrowth, there is a need for a multi-degree central office (CO) node todynamically add/drop a large number of colorless, directionless, andcontentionless (CDC) wavelengths [2]. As an example, consider an8-degree CO with 96λ's from/to each of its 8 directions, a 50% add/dropratio would require five CO to add/drop 96·8·50%=384%'s. To add/dropsuch a large number of λ's, modular and scalable M×N multicast switches(MCS's) are believed to offer the most economical solution today.Herein, are presented methods to optimize the architecture of anMCS-based flexible-grid CDC ROADM such that its cost is minimized. Oneembodiment is shown in FIGS. 18-23.

FIG. 18A depicts MCS-based flexible-grid CDC ROADM card 1800 with frontside 1802, heat sink 1804, line card 1806, multicast switch module 1808,isolator/EDF tray 1810, fiber management tray 1812, and cover fibermanagement tray 1814. FIG. 18B is another side perspective view of thecard 1800 further showing fiber 1816, fiber management tray 1818, andprotector fiber splicing 1820. FIG. 19 is a plan view of a subassembly1801 of card 1800, showing keep-out area 1822. FIG. 20 is a perspectiveview of subassembly 1801 showing multicast switch mounts 1808 in placeever keep-out area 1822. FIG. 21 is a plan view of subassembly 1801 withisolator/GFF/EDF tray 1824, fiber 1816, and protector fiber splicing1820. FIG. 22 shows subassembly 1801 with fiber management tray 1118.Heat sink 1804 is placed near the top of the card. Input/output fiberscome out at an angle on the bottom of the MCS/TSPL module and are routedto the face-plate bulkheads. FIG. 23 depicts a rough layout for aplanar-integrated 4×16 expandable MCS, including some possible relativedimensions and other rough details, although specific layouts generallyinvolve specific preferences of a designer.

Basic CDC ROADM Architecture Based on M×N Multicast Switches

A basic M×N MCS 2400 is shown in the gray card of FIG. 24 a [3], withM=8 and N=16, as an example. Each of 8 MCS input ports 2402 is connectedto one of the eight directions. An MCS provides “colorless” drop withoutpre-filtering to an external coherent receiver (CR), which has abuilt-in tunable laser serving as a local oscillator, or alternativelyan external tunable channel filter can isolate a single wavelengthchannel to be provided to a standard direct-detection receiver. Atunable channel filter could increase the overall cost significantlyunless an extremely low cost technology can be developed, and thereforeour focus will be on coherent systems only. An MCS is “directionless”because any output port can drop any input signals front any directionvia a 1×M selection switch. An MCS is also “contentionless” because each1×M switch can only select signals from a particular direction, so forthe defined operation precludes λ's of the same color from differentdirections from colliding with each other. Finally, an MCS also has thefeature of “flexible grid” due to the filter-less feature of a CR, whichalso makes MCS-based ROADM inherently low cost.

A standalone MCS cannot complete the multi-degree CDC add/drop functionsowing to a few reasons. First of all, the loss of 1×N splitters may becompensated by erbium-doped fiber amplifiers (EDFAs). Secondly, due tothe limited output ports per MCS (N≧24 using today'splanar-lightwave-circuit or MEMS technology), multiple MCS cards must beadded in a pay-as-you-grow manner. For a total of 384λ's, 384/16=24 8×16MCS cards need to be used. As a result, between each drop fiber and 24MCS cards, a 1×24 WSS can be used to split the incoming 96λ's from eachdirection into its 24 output ports, and most importantly, to control themaximum number of λ's per output port (N_(WSS,max)). A basic CDC ROADMarchitecture may have a lap layer of 8 1×24 WSS's, a second layer of 192EDFAs, and a bottom layer of 24 8×16 MCS cards, to enable 384λ's droppedfrom any of the 8 directions without contention. Hot-standby protectioncan be achieved by adding an extra amplified MCS card to FIG. 24 a, sothat in the event that any of the active amplified MCS cards fail, thetop-layer WSS's can re-route the corresponding traffic to the protectioncard. A similar architecture is needed for the add direction. Note thatin this basic architecture, the large member of EDFAs and the largeport-count WSS could cause cost, space, and power consumption issues.

The parameter N_(WSS,max) mentioned above must meet the followingconditions: (i) N_(WSS,max)≦N_(CR), where N_(CR) is the maximum numberof coincidental λ's that can be handled by a CR with acceptably low OSNRpenalty [4]—this condition is required because all N_(WSS,max)λ's wouldbe received by a CR. (ii) N_(WSS,max)=N_(split), where N_(split) is thetotal number or post-EDFA spilt ports (N_(split)=16 in FIG. 24 a)—thiscondition is required to cope with the worst non-uniform traffic whenλ's arrive into an amplified MCS from only one direction, and each CRselects a unique wavelength. If N_(WSS,max)>N_(split) it implies(N_(WSS,max)−N_(split)) λ's have no output port to exit, whileN_(WSS,max)<N_(split) implies when the incoming λ's continue to flow infrom only one direction, one has to add new amplified MCS cards evenwhen there are still empty ports left in the original card. Therefore,the ideal condition is N_(WSS,max)=N_(split). (iii) Each EDFAs shouldprovide N_(WSS,max)λ's with sufficient optical power per λ (P_(rec)) ata CR, which has a typical receiver sensitivity of −20 dBm for 100GDP-QPSK. Combining conditions (i) and (ii), the expression may be madethat:N _(split) =N _(WSS,max) ≦N _(CR), for all EDFAs in an amplified MCScard.  (1)From condition (iii), therefore:P _(rec) =P _(EDFA)−10·log(N _(WSS,max))−10·log(N _(split))−IL_(excess)  (2)where P_(EDFA) is the total output power of each EDFA, and IL_(excess)is the MCS excess loss over 10·log(N), which could range from 3 to 6 dB.Eqs (1) and (2) imply that every EDFA in FIG. 24 is designed to handlethe worse-case non-uniform traffic, i.e., N_(WSS,max) channels of λ'sand consequently requiring higher power EDFAs and higher cost. Theeffect of non-uniform traffic can be expressed in terms non-uniform touniform traffic ratio η. For example, in FIG. 19 a, a uniform trafficwith 50% drop ratio gives us N_(WSS,unif)=96·50%/24=2, and thereforeη=N_(WSS,max)/N_(WSS,unif)=16/2=8.CDC ROADM Architecture Based an M×N Multicast Switches

FIG. 24 shows an 8-deg, 50% drop CDC ROADM: FIG. 24 a using 8 1×24 WSS's2404 and 24 amplified 8×16 MCS's 2406; FIG. 24 b using 8 1×12 WSS's 2408and 12 amplified dual-8×16 cards by inserting a 1×2 splitters 2412between EDFAs 2411 and dual-MCS's 2414. Block labeled CR=deplore acoherent receiver. Further improvement of the basic architecture in FIG.24 a for cost and size reduction is described as follows. From a coststandpoint, per add/drop port cost in a CDC ROADM is given asPer add/drop port cost=Per MCS add/drop port cost+EDFA cost/J+WSS portcost/K  (3)

In the example shown in FIG. 24 a, J=2 (every 8 EDFAs correspond to 16MCS add/drop ports) and K=2 (every 8 WSS add/drop ports correspond to 16MCS add/drop ports). The question now is whether J and K can be furtherincreased by increasing N_(split), so that more MCS add/drop ports canshare the higher layer EDFA and WSS cost. One approach is to increasethe add/drop port count of an MCS, but the maximum port count per MCS is≦24 today. Another approach is to insert 1×2^(L) (L=1, 2, 3, . . . )splitters between EDFAs and MCSs (so that N_(split)=N×2^(L)), shown inFIG. 1 b (L=1). Note that the addition of a I×2 splitter layer in FIG.24 b effectively makes the amplified MCS an 8×32 module, which enablesthe reduction of the number of amplified MCS cards and WSS ports by 50%,as can be observed by comparing FIGS. 24 a and 24 b. On the other hand,N_(split) cannot be too large—its upper bound can be obtained from Eq.(2) by letting N_(split)=N_(WSS,max) and P_(EDFA)=21 dBm, and the resultis shown in FIG. 25. Assuming P_(rec)=−16 dBm (this gives a 4 dB margintor a typical CR), we see that N_(split) can be ≦32 (e.g., usingdual-8×16 MCS's with 1×2 splitters) or ≦48 (e.g., using dual-8×24 MCS'swith 1×2 splitters), depending on the MCS excess loss.

A typical N_(CR)≦12˜16 today, and therefore N_(CR) in Eq. (1) actuallysets a more severe constraint on N_(split) than Eq. (2)—even though,this constraint may be relaxed via future proprietary digital signalprocessing algorithms. Eq. (1) also indicates that N_(split) andN_(WSS,max) are tightly coupled such that every time N_(split) doubles,P_(rec) is reduced by 6 dB rather than 3 dB. There are, however, a fewarchitectural approaches to relax the constraints on N_(split) set byEq. (1). The first is to use a tunable filter array (TFA) between MCS'sand CR's to ensure the number of received λ's at a CR is ≦N_(CR) eventhough N_(split)=N_(WSS,max) is large [5]. The disadvantage of thisapproach is that the cost of TFA adds directly to the per drop portcost, and the TFA's ˜2 dB insertion loss could effectively increase theEDFA cost. The second approach is to let the EDFAs in an amplified MCScard share one or two pump lasers via a tunable 1×M splitter, so thatthe majority of the EDFAs do not need to amplify a full load ofN_(WSS,max)λ's, thus saving cost [3]. The disadvantage of this method isthat it is difficult to adjust the pump sharing among EDFAs flexibly fordynamic λ add/drop. Also, this method does not allow a large N_(split)to increase K in Eq. (3). Our approach is to decouple N_(split) fromN_(WSS,max) in Eq. (1) so N_(split) can be independently increased. Asshown in FIG. 26, that depicts an MCS-based CDC ROADM with an OXC loadbalancer (100% drop) 2448, an N×N (N=64) optical cross-connect (OXC)2450 is inserted between WSS 2452 and EDFA 2452 layers, and N_(split) isdramatically increased to 4×24=96. The OXC serves as a “load balancer”(LB), i.e., even when the first 96λ's are arriving from only onedirection (say direction West), the load balancer will re-shuffle the 8West WSS output ports (with 12λ's per port) to the front row so thatonly one, instead of multiple, amplified MCS card needs to be used. TheROADM in FIG. 20 has the following features: (a) it allows 100% add/dropso that its cost can be shared by up to 784 add/drop ports; (b) itexhibits an excellent η of unity; (c) it uses a low number of coincidentchannels at a CR (N_(WSS,max)=12) and its insertion loss of ˜2 d8 can beeasily compensated by the following EDFAs without increased cost; (d) itincreases the post-EDFA split significantly to 96, but still operates ata reasonable P_(rec)=−15 dBm (obtained from Eq. (2) with P_(EDFA)=21 dBmand IL_(excess)=5 dB). Also, J and K in Eq. (1) am now increased to 12,which results in the lowest overall material cost, as shown in FIG. 27(see “8×96+LB”). Also shown in FIG. 27 is the relative cost of othertypes of MCS using the conventional approaches with 50% add/drop. Themain reason that a load-balancer can reduce the total cost of an 8×16MCS-based ROADM by ˜70%, for example, is because in the drop direction192 15 dBm EDFAs is reduced to 64 21 dBm EDFAs, and the number of WSSports is reduced from 192 to 64. For a fair comparison in FIG. 27, 8×12and 8×16 MCS's cannot quite achieve 50% add/drop because 1×32 and 1×24WSS are not available today, while 8×24 and 8×32 MCS's could encountercertain OSNR penalties due to the fact that its N_(WSS,max) exceedstoday's N_(CR) of 12˜16.

FIG. 28 depicts the ROADM integrated into various networkconfigurations. The use of the expandable multicast switches providedesirable routing flexibility. ROADM 2800 has programmable splitters2802 that are programmable to avoid distributing optical power intodormant channels and the associated waste. The programmable splitters2802 can dynamically reconfigure power distribution for, e.g., singledirection traffic 2804, with 2102 a depleting a splitting effect.Splitters 2802 are programmable for, e.g., traffic from all directionsuniformly, 2806, with 2802 b, 2802 b′ depicting exemplary signal flow.Splitters 2802 are programmable for arbitrary traffic, 2808, with 2802c, 2802 c′, 2802 c″ depicting the same.

FIG. 20 depicts an embodiment of a continuous switch used as aprogrammable splitter. MZI-based programmable splitter 2900 has an inputN, 2902, dynamically split among 16 outputs 2804. Such a splitter can beused as a splitter tree for a multicast switch, such as for the specificembodiments described above. In general, a continuous-range opticalswitch can be made i.e. from Mach-Zehnder interferometer accepting acontinuous range of drive voltages to its phase shifter. Opticalswitches for the architectures described herein, such as 1×2, 2×1 and2×2 switches, can similarly be based on Mach-Zehnder Interferometerstructures. Alternative optical switch designs can be based on MEMstechnology and/or other mechanical structures, e.g. piezoelectric basedstructures, electro-optical effects, magneto-optical effects,combinations thereof of the like. In general, optical switch designs areknown in the art and are under continual further development.

FIG. 30 depicts an alternative embodiment of the ROADM design of FIG. 24a. In this embodiment, ROADM 3000 comprises a pluggable amplifier card3002 placed between the wavelength selective switches (WSS) 3004 and theMCS cheeks 3006. MCS circuits 3006 comprise splitters 3008 and switchbanks 3010. The amplifiers can amplify each input signal into the MCS.FIG. 31 depicts a variation on the embodiment with low power amplifiersfor use with networks with traffic from all directions uniformly,referring to FIG. 28.

FIG. 32 depicts an embodiment of a ROADM with a set of 8 1×20 WSS 3020contacted to inputs 3021 providing input into OXC cross connect switches3022 for load balance. A pluggable amplifier pool 3024 providesamplification of the signals form the WSS. In some embodiments, aportion of the output 3030 from the OXC 3020 can be directed to inputports of MCS 3028, and a second portion of the outputs 3032 of the OXCcan be directed to expansion-in ports 3034 of the MCS, which areconnected to bypass light paths 3036 leading to bypass switches 3038.This embodiment includes providing fully automatic and flexibleswitching.

A ROADM design using alternative routes within the ROADM is depicted inFIG. 33. The architecture of panel (c) is contrasted with a ROADM withcontention mitigation based on pre-installed large number of DWDMtransponders and optical transport network switch ports is depictedschematically in panel (a) and based on client side fiber cross connectsof panel (b). While the expandable switches described herein can beeffectively used in any of these architectures, the design in panel (c)involves rerouting through contention reduction banks of switches tomitigate contention down to probabilities of little consequence. Thearchitecture of an embodiment of the ROADM is shown in FIG. 34.

As shown in FIG. 34, contention reduction banks can comprise up to N−1contention mitigation (CM) switch structures, in which N is the numberof inputs into the ROADM. Each CM switch structure can comprise N×Mswitches, such as cross connect switches or other similar switchfunctions. As shown its FIG. 34, each switch structure comprises 1×8power couplers and a 1×16 power switch, that provide cross connectfunctionality. The ROADM further comprises M drop banks. As shown inFIG. 34, output from the WSS go to M (1×N) power couplers that provideinput into MCS switches, and output from the contention banks are alsodirected to MCS inputs. In alternative embodiments based on theexpandable MCS switch designs described herein, outputs from thecontention banks can be directed to expansion-in ports or the MCSswitches and the outputs of the WSS can be directly directed to theinputs of the MCS switches without using the couplers. The blocking rateas a function of offered load can be effectively no contention, e.g.,much less than 10⁻⁷ blocking rate with a larger number of contentionbanks, specifically, 5-7 contention banks.

Ring optical networks can provide for considerable robustness since if abreak in a line occurs, signal transmission can take place alternativelythrough a parallel ring regardless of the location of a break. Aconceptual diagram of a ring networks with two parallel optical pathsconnecting a set of nodes is shown in FIG. 35. Such a ring network canbe used, for example as a network metro edge with roughly 4-8 ports pernode, 88 DWDM wavelengths, with colorless ROADM. In some embodiments,the ring network can be used as a centralized ring network with a mainnode and associated subnodes. Potential node structure is shown in FIG.36.

Referring to FIG. 36, a node 3602 comprises two parallel structures forperforming ADD and DROP functions. Each parallel optical line 3604 and3606 connects with a 1×2 WSS to the ADD (3608, 3610) and to the DROP(3612, 3614) sides of the node. The ADD side of the node comprises twoMCS 3620, 3622 connected to WSS 3608, 3610, respectively, and MCS 3620,3622 connect at a set of 2×1 bypass switches 2624. Similarly, the DROPside of the node comprises two MCS 3640, 3642 connected to WSS3612,3614, respectively, and MCS 3640, 3642 connect at a set of 2×1bypass switches 2644. If an integrated expandable MCS is used, theoutput from one of the pairs of MCS (3620+3622 or 3640+3642) can bedirected to expansion in ports of the other MCS switch to make use ofthe bypass switches of the expandable switch to provide desiredfunctionality.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

References incorporated herein by reference: [1] M. Feuer, et al.,Optical Fiber Telecommunications, Vol. B, Systems and Networks, Chapter8, 2008: [2] S. Gringeri, et al., IEEE Commn. Mag., p. 40, July 2010;[3] S. Zhong and J. Bao, US patent application publication, US2009/0067845; [4] L. Nelson, et al., J. Lightwave Technol., p. 2933,2010; [5] T. Watanabe, et al., OFC/NFOEC, paper OTuD3, 2011.

What is claimed is:
 1. An optical switching device with expansionconnections comprising a photonic integrated circuit, the photonicintegrated circuit comprising N input optical ports where N>1, an inputlight-path associated with each input port, M optical output ports whereM≧1, an output light-path associated with each output port, a bypassoptical switch block associated with each output port, P expansion-inports where P≧1, an expansion light-path associated with eachexpansion-in port and connecting with an associated bypass switch block,a plurality of optical switching elements and associated light-pathsforming a network of connections between the input light-paths and aby-pass switch block associated with an output light-path.
 2. Theoptical switching device of claim 1 wherein P=mM, where m is an integer≧2 and wherein the bypass optical switch block comprises (m+1)×1 opticalswitching device.
 3. The optical switching device of claim 1 wherein P=Mand wherein the bypass optical switching block comprises a 2×1 opticalswitch.
 4. The optical switching device of claim 1 further comprising atree structure of optical splitters and associated plurality of opticallight-paths, wherein the plurality of optical switching elements areorganized into groups with each switch group being associated with thebypass switch associated with an output light-path, wherein the splitoptical light-paths provide inputs into the switch groups, and whereineach input to a switch group is connected to a light path associatedwith a distinct tree of splitters.
 5. The optical switching device ofclaim 4 wherein the photonic integrated circuit has an architecture of amulticast switch with a configuration to distribute an optical signalfor each of M output port bypass switches that is selected from any ofthe N input ports.
 6. The optical switching device of claim 4 whereineach input is connected to K branches with K≧M, where if K>M, K−Moptical pathways are dormant.
 7. The optical switching device of claim 4wherein each input is connected to K branches with K<M and wherein theswitching elements are configured to selectively direct a signal from aninput to a subset of K outputs.
 8. The optical switching device of claim4 wherein a switching block associated with a particular bypass switchconnected with an output comprises N−1 sequentially aligned 2×1 opticalswitching elements.
 9. The optical switching device of claim 4 wherein aswitching block associated with a particular bypass switch connectedwith an output comprises L {L=smallest integer≧log₂(N)} sequentiallevels of 2×1 optical switching elements.
 10. The optical switchingdevice of claim 1 wherein the plurality of optical switching elementsand associated light paths have a conceptual rectangular matrix ofswitches providing connections between each input light paths with eachoutput light paths.
 11. The optical switching device of claim 1 furthercomprising a set of Q expansion-out optical ports, an expansion-outlight path associated with each expansion-out port and a bypass opticalswitch connecting an input light path with an expansion-out light pathand the network of optical switching elements and associated lightpaths.
 12. The optical switching device of claim 1 wherein the bypassswitches are continuously adjustable.
 13. The optical switch device ofclaim 1 wherein the photonic integrated circuit comprises waveguideintegrated optical circuit on a planar substrate.
 14. The optical switchdevice of claim 1 wherein the optical switching elements comprise 2×1optical switches.
 15. The optical switch device of claim 1 wherein theoptical switching elements comprise 2×2 optical switches.
 16. Theoptical switching device of claim 1 further comprising an opticalamplifier optically coupled to an input line or to an output line. 17.An optical switching device with expansion connections comprising aphotonic integrated circuit, the photonic integrated circuit comprisingN input optical ports where N≧1, an input light path associated witheach input port, M optical output ports where M>1, an output light pathassociated with each output port, a bypass optical switch blockassociated with each input port, Q expansion-out ports where Q≧1, anexpansion light path associated with each expansion-out port andconnecting with an associated bypass switch block, a plurality ofoptical switching elements and associated light paths forming a networkof connections between the by-pass switch block associated with an inputlight path and the output ports.
 18. The optical switching device ofclaim 17 wherein the plurality of optical switching elements andassociated light paths have a conceptual rectangular matrix of switchesproviding connections between each input light path and each outputlight path.
 19. The optical switching device of claim 17 furthercomprising a tree structure of optical combiners and associatedplurality of optical light-paths, wherein the plurality of opticalswitching elements are organized into groups, each switch group beingassociated with a light-path connected to an input port, wherein eachoutput of a switch group is coupled to a branch of a distinct opticalcombiner tree.
 20. The optical switching device of claim 19 wherein thephotonic integrated circuit has an architecture of a multicast switchwith a configuration to distribute an optical signal for each of the Moutput ports that is selected from any of the N input port bypassswitches.
 21. The optical switching device of claim 17 wherein Q=N andwherein the bypass optical switching block comprises a 2×1 opticalswitch.
 22. The optical switching device of claim 17 wherein the bypassswitches are continuously adjustable.
 23. The optical switch device ofclaim 17 wherein the photonic integrated circuit comprises waveguideintegrated optical circuit on a planar substrate.
 24. The opticalswitching device of claim 17 further comprising an optical amplifieroptically coupled to an input line or to an output line.
 25. Anexpandable optical switch device for dynamically configuring theinterconnections between a selected number of optical input ports and Moptical output ports, the switch device comprising Z optical switchingmodules (Z≧2) with optical inter-connections to form a configurationhaving an initial module, a terminal module and optional intermediatemodules, each optical switching module L comprising N_(L) input portsand M output ports and desired switching capability between the inputports and output ports with the sum of N_(L) equal to the selectednumber of input ports, wherein each optical switching module that is notan initial module having a set of expansion in ports coupled throughbypass switches to respective output ports and wherein each opticalmodule that is not a terminal module having a set of output portscoupled to expansion in ports of another module.
 26. The expandableoptical switch device of claim 25 wherein each switching module furthercomprises a tree structure of optical splitters and associated pluralityof light-paths and a plurality of optical switching elements andassociated light-paths forming a network of connections between opticalsplitters and the bypass switches.
 27. The optical switching device ofclaim 26 wherein the photonic integrated circuit has an architecture ofa multicast switch with a configuration to distribute an optical signalfor each of the M output port bypass switches that is selected from anyof the N_(L) input ports.
 28. An expandable optical switch device fordynamically configuring the interconnections between N optical inputports and a selected number of optical output ports, the switch devicecomprising Z optical switching modules (Z≧2) with opticalinter-connections to form a configuration having an initial module, aterminal module and optional intermediate modules, each opticalswitching module L comprising N input ports and M_(L) output ports anddesired switching capability between the input ports and output portswith the sum of M_(L) equal to the selected number of output ports,wherein each optical switching module that is not a terminal modulehaving a set of expansion out ports coupled through bypass switches torespective input ports and wherein each optical module that is not aninitial module having a set of input ports coupled to expansion outports of another module.
 29. The expandable optical switch device ofclaim 28 wherein each switching module further comprises a treestructure of optical splitters and associated plurality of light-pathsand a plurality of optical switching elements and associated light-pathsforming a network of connections between optical splitters and theoutput ports.
 30. The optical switching device of claim 29 wherein thephotonic integrated circuit has an architecture of a multicast switchwith a configuration to distribute an optical signal for each of theM_(L) output port bypass switches that is selected from any of the Ninput port bypass switches.